Fluorohydrocarbon elastomers

ABSTRACT

A FLUOROHYDROCARBON ELASTOMER COMPOSITION HAVING IMPROVED LOW TEMPERATURE PROPERTIES IS PROVIDED BY INCLUDING IN THE COMPOSITION AS PLASTICIZER A FLUOROSILICONE POLYMER WHICH HAS BEEN MODIFIED BY TREATMENT WITH AN AMINE COMPOUND OF FORMULA H2N(R.NH)NH, WHERE R IS A DIVALENT LOWER ALKANE CHAIN CONTAINING NOT MORE THAN EIGHT CARBON ATOMS, AND N IS AN INTEGER FROM ONE TO FIVE, AN AN ORGANIC PEROXIDE FREE RADICAL SOURCE, TO HAVE A SPECIFIC VISCOSITY IN THE RANGE 0.03 TO 0.06. PREFERABLY THE AMINE COMPOUND IS TRIETHYLENE TETRAMINE AND THE ORGANIC PEROXIDE FREE RADICAL SOURCE IS 2.5-DIMETHYL-2,5-DITERTIARY BUTYLPEROXYHEXANE. IN A TYPICAL EXAMPLE THE CLASH AND BERG TEMPERATURE OF A TYPICAL VINYLDENE FLUORIDE/HEXAFLUOROPROPYLENE COPOLYMER IS REDUCED FROM -17* C. TO -32* C.

United States Patent US. Cl. 260-4227 11 Claims ABSTRACT OF THEDISCLOSURE A fiuorohydrocarbon elastomer composition having improved lowtemperature properties is provided by including in the composition asplasticizer a fluorosilicone polymer which has been modified bytreatment with an amine compound of formula H N(R-NH) H, where R is adivalent lower alkane chain containing not more than eight carbon atoms,and n is an integer from one to five, an an organic peroxide freeradical source, to have a specific viscosity in the range 0.03 to 0.06.Preferably the amine compound is triethylene tetramine and the organicperoxide free radical source is2,5-dimethyl-2,S-ditertiarybutylperoxyhexane. In a typical example theClash and Berg temperature of a typical vinylidenefluoride/hexafluoropropylene copolymer is reduced from 17 C. to 32 C.

The present invention is concerned with fiuorohydrocarbon elastomericcompositions.

Flurohydrocarbon elastomers are well known and have advantageousproperties regarding stability at high temperatures as exemplified byViton (registered trademark) elastomers. However such materials do notretain their elastomeric properties to particularly low temperatures.For example a widely used fiuorohydrocarbon elastomer, Viton B(registered trademark), shows relatively poor elastomeric properties at-16 C. and cannot in general be used below that temperature insituations where resilience is required.

It is an object of the present invention to provide a modification offiuorohydrocarbon elastomer compositions by which the elastomericproperties may be retained to lower temperatures than with theunmodified compositions whilst still retaining to at least a substantialextent the long term stability of the vulcanizate at elevatedtemperatures.

In accordance with the present invention a fiuorohydrocarbon elastomercomposition includes fiuorohydrocarbon elastomer, a finely dividedmagnesia filler, a modified (as hereinafter defined) fluorosiliconepolymer having a specific viscosity in the range 0.03 to 0.06, and acuring agent for the said fiuorohydrocarbon elastomer.

The specific viscosity of fluorosilicone polymers as quoted in thepresent specification are determined in solution in ethyl acetate at aconcentration of 0.1 g./ 100 ml. at a temperature of 28 C.

Preferably the modified fluorosilicone polymer is poly-(methyltrifluoropropylsiloxane) which includes suflicient vinyl groupsto aid crosslinking, normally 0.10 to 0.20 mole percent of vinyl groups.

Fluorosilicone polymers as normally supplied have specific viscositiesgreater than those required for inclusion in compositions of the presentinvention. For example, polymethyl-3,3,3-trifluoropropylsiloxane(obtainable from Dow Corning Co. as LS 420) as normally supplied has aspecific viscosity of 0.089 and in accordance with an aspect of thepresent invention a process for the modification of fluorosiliconepolymers is provided.

"Ice

For the purpose of the present specification the term modifiedfluorosilicone polymer means a fluorosilicone polymer which has beencompounded with a proportion of an amine compound of formula HN(R-NH),,H where R is a divalent lower alkane chain containing not morethan eight carbon atoms, and preferably two carbon atoms, and n is aninteger of one to five, preferably three, and a proportion of an organicperoxide free radical source, which is preferably 2,5-dimethyl 2,5ditertiarybutylperoxyhexane, and heated to an elevated temperature inthe range 150 C. to 200 C. under pressure for a time suflicient todepolymerize the fluorosilicone polymer so that its specific viscosityfalls to within the range 0.03 to 0.06.

It will be understood by those skilled in the art that the time ofheating and temperature of heating are interdependent and that the sameresult may be obtained by using for example a relatively low temperaturetogether with a relatively long time as with a relatively hightemperature and a relatively short heating time.

In preferred reactions in accordance with this aspect of the presentinvention the amine compound is triethylene tetramine and is used in aproportion of up to 1.0 part by weight per parts by weight offluorosilicone polymer and the organic peroxide free radical source is2,5-dimethyl 2,5 ditertiarybutylperoxyhexane present to the extent of upto 20 parts by weight per 100 parts by weight of fluorosilicone polymer.

It is believed that the fluorosilicone polymer acts as a plasticizer forthe fiuorohydrocarbon elastomer thereby lowering the temperature atwhich the fiuorohydrocarbon elastomer composition ceases to havesufiicient elastomeric properties to be useful. It is also believed thatat least some of the fluorosilicone polymer is bonded into thefiuorohydrocarbon network because although fluorosilicone polymer istotally soluble in ethyl acetate, only a proportion of thefluorosilicone can be leached out by ethyl acetate.

The term fiuorohydrocarbon elastomer is used in the presentspecification to mean a polymer of fluorine substituted ethylenicallyunsaturated hydrocarbons having elastomeric properties and includescopolymers, particularly copolymers of vinylidene fluoride and one ormore halogenated olefins for example, hexafluoropropylene,pentafluoropropylene, tetrafluoroethylene and chlorotrifluoroethylene.

Specific copolymers to which the present application may be appliedinclude the copolymer of vinylidene fluoride and hexafluoropropylenecontaining 70 to 30, and preferably '60, mole percent of vinylidenefluoride and 30 to 70, preferably 40, mole percent ofhexafluoropropylene, sold for example under the trade name of Viton A,similar copolymers of vinylidene fluoride and hexafluoropropylenecontaining minor proportions of tetrafluoroethylene, sold for exampleunder the trade name of Viton B and copolymers of vinylidene fluoride apentafluoropropylene sold under the trade name of Technofion.

Advantageously fiuorohydrocarbon elastomer compositions of the presentinvention include for each 100 parts by Weight of fiuorohydrocarbonelastomer; 5 to 30 parts by weight of finely divided magnesia filler, 10to 40 parts by weight of modified fluorosilicone polymer having aspecific viscosity in the range 0.03 to 0.06 and 0.5 to 5.0 parts byweight of curing agent.

The particular curing agent employed does not constitute part of theinvention and may be any curing agent such as is commonly used in theart to cure fiuorohydrocarbon elastomer compositions, for exampledicinnamylidene-1,6-hexanediene or 1,6-hexane diamine carbamate orpossibly the triethylene tetramine/p-phenylene 3 diamine mixturedisclosed in UK. patent specification No. 1,161,410.

The composition may be cured by use of customary procedures.

It is to be understood that other materials, e.g. carbon black andpigments, such as are normally added to elastomer compositions may beadded to the compositions of the present invention.

Fluorohydrocarbon elastomer compositions of the present invention may becompounded by conventional means upon conventional rubber processingmachinery and, in accordance with a second aspect of the presentinvention, a process for the production of a fiuorohydrocarbon elastomerwith a finely divided magnesia filler, a modified (as hereinbeforedefined) fluorosilicone polymer having a specific viscosity in the range0.03 to 0.06 and a curing agent for the said fluorohydrocarbon elastomerand curing the said composition. In particular processes of this aspectof the present invention the proportions of the various components ofthe fiuorohydrocarbon elastomer may be varied as hereinabove set forth.

There will now be described, by way of example only, thedepolymerization of a fluorosilicone polymer to material of low specificviscosity and the compounding of such material with fluorohydrocarbonelastomer to produce compositions having improved low temperatureproperties.

EXAMPLE 1 Depolymerization of fluorosilicone The formulation: Parts byweight Methyltrifiuoropropylsiloxane (LS 420) 100 2,5 dimethyl 2,5ditertiarybutylperoxyhexane (Varox) Triethylene tetramine (TETA) 0.5

was thoroughly compounded on a standard 6" x 2" rubber mill, sheeted offand the sheet then placed in a mould. The mould was slightly overfilledso that internal pressure would be applied when the mould was closed.The mould was placed in a heated press at 160 C. and kept for 1 hour atthe end of which time the mould and press were allowed to cool underpressure and the material, which will hereinafter be referred to as DPLS 420, removed. This material had a specific viscosity as hereinbeforedefined of 0.045.

This depolymerized fiuorosilicone was used to prepare fluorohydrocarbonelastomer compositions with the properties described in the followingexamples.

EXAMPLE 2 The following formulation was compounded in a standard manner:Parts by weight Fluorohydrocarbon elastomer (vinylidenefluoride/hexafiuoropropylene copolymer ECD-487) 100 Magnesia-finely divided MTCarbon Black DP LS 420 1,6-hexane diamine carbamate (Diak 1) 3.0

and press cured at 160 C. for 1 hour followed by an oven post cure of 24hours at 200 C.

The properties of this composition are compared in Table 1 with theproperties of the parent fluorohydrocarbon elastomer compounded andvulcanized according to normal practice.

4 The property M is defined as the force required to extend the rubberby 100% and the Clash & Berg temperature is determined by means wellknown in the art and in general defines the lowest temperature at whichan elastomer displays useful elastomeric properties.

EXAMPLE 3 The following formulation was compounded in a standard manner:

Parts by weight Fluorohydrocanbon elastomer (Viton Bvinylidenefluoride/hexafluoropropylene copolymer) 100 Magnesiafinely divided 15 DPLS 420 30 Dicinnamylidene-1,6-hexane diamine (Diak 3) 1.5

and press cured at 150 C. for 1 hour with no post cure.

The properties of this composition are compared in Table 2 with theproperties of the parent fiuorohydrocarbon elastomer compounded andvulcanized according to normal practice.

TABLE 2 Modified compo- Viton B sition Ultimate tensile strength, p.s.i2, 177 1, 317 M 100, p.s.i 423 103 Ultimate strain, percent 500 863Clash & Berg temperature, C 17 32 EXAMPLE 4 The following formulationwas compounded in a standard manner:

Parts by weight Viton B 100 Magnesia-finely divided 15 DP LS 420 30 Diak3 1.5

and press cured at 150 C. for 30 minutes followed by an oven cure of 24hours at 200 C.

The properties of this composition are given in Table 3 and may becompared with the'properties of the parent fluorohydrocarbon given inTable 1.

TABLE 3 Ultimate tensile strength p.s.i. 2350 M 100 193 Ultimate strainpereent 535 Clash & Berg temperature C --27 The Clash & Berg temperatureof this fluorohydrocarbon elastomer composition was unchanged after ithad been heat aged at 200 C. for 7 days.

Further tests were carried out on this formulation; the resistance tohot kerosene is set forth in Table 4 immediately below and the resultsof stress relaxation tests are set forth in Table 5 and of compressionset tests in Table 6.

Swelling ratio is defined as the ratio of the dry weight to the swollenweight of a sample of rubber.

The very low fractions soluble in acetone and the virtually unchangedswelling ratio in acetone after exposure to kerosene at C. for up to1104 hours indicates that the rubber vulcanizate structure is unchanged.By contrast in an identical test a commercial fluorosilicone iscompletely brittle after about 500 hours.

Table 5 reports the results of continuous and intermittentstress-relaxation tests carried out in air at 110 C. and 120 C.

TABLE 5 Percent Percent change change Percent oi overall in Percent ofoverall in network network network network Time in hours broken densitybroken density TABLE 6 Percent set Time in compression, hours The ratherhigh compression set values at 24 hours are typical of low modulusfluorocarbon elastomers and are largely a result of rather slow physicalrelaxation processes.

What we claim is:

1. A fluorohydrocarbon elastomer composition comprising 100 parts byweight of fluorohydrocarbon elastomer,

5 to 30 parts by weight a finely divided magnesia filler,

10 to 40 parts by weight of a fluorosilicone polymer and 0.5 to 5 partsby weight of a curing agent for the said fluorohydrocarbon elastomer,the said fluorosilicone having been modified by compounding with aproportion of an amine compound of formula H H(R-NH) H where R is adivalent lower alkane chain containing not more than eight carbon atoms,and n is an integer from one to five, and a proportion of an organicfree radical source, and

heating at an elevated temperature in the range 150 C.

to 200 C. under pressure for a time sufficient to depolymerize thefluorosilicone polymer to a specific viscosity within the range fromabout 0.03 to about 0.06 determined in a solution of ethyl acetate at aconcentration of 0.1 g./100 ml. at 28 C.

2. A composition as claimed in claim 1 wherein the fluorohydrocarbonelastomer is selected from the group consisting of copolymers ofvinylidene fluoride with one or more comonomers from the grouphexafluoropropylene, pentafluoropropylene, tetrafluorethylene andchlorotrifluoroethylene.

3. A composition as claimed in claim 1 wherein the curing agent isselected from the group consisting of 10 proportion of up to one part byweight per hundred parts by weight of fluorosilicone polymer.

6. A composition as claimed in claim 1 wherein the organic peroxide freeradical source is 2,5-dimethyl2, 5- ditertiarybutylperoxyhexane and ispresent to the extent of up to 20 parts by weight of fluoro-siliconepolymer and the amine compound is triethylene tetramine present to theextent of up to 0.5 part by weight per hundred parts by weight offluorosilicone polymer.

7. A composition as claimed in claim 1 after cure.

8. A process for the modification of a fluorosilicone polymer whichincludes the step of compounding the said fluorosilicone polymer with aproportion of an amine compound of formula H H(R-NH) H where R is adivalent lower alkane chain containing not more than eight carbon atoms,and n is an integer from one to five, and a proportion of an organicfree radical source, and heating at an elevated temperature in the rangeof from about C. to about 200 C. under pressure for a time sufficient todepolymerize the fluorosilicone polymer to a specific viscosity withinthe range 0.03 to 0.06.

9. A process as claimed in claim 8 wherein the amine compound istriethylene tetramine and is used in a proportion of up to one part byweight per hundred parts by weight of fluorosilicone polymer.

10. A process as claimed in claim 8 wherein the organic peroxide freeradical source is 2,5-dimethyl-2,S-ditertiarybutylperoxyhexane and ispresent to the extent of up to 20 parts by weight of fluorosiliconepolymer and the amine compound is triethylene tetramine present to theextent of up to 0.5 part by weight per hundred parts by weight offluorosilicone polymer.

11. A process as claimed in claim 8 wherein the fluorosilicone polymeris poly(methyltrifluoropropylsiloxane) which includes 0.10 to 0.20 molepercent of vinyl groups.

References Cited UNITED STATES PATENTS 3,632,788 l/1972 Stivers 260 30.8R 3,630,982 12/ 1971 Matherly 260-29.1 SB 3,192,175 6/1965 Russell26029.1 3,122,521 2/1964 Pierce 26046.5 3,538,028 1l/1970 Morgan 26023MORRIS LIEBMAN, Primary Examiner R. ZAITLEN, Assistant Examiner US. Cl.X.R.

